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Three neonicotinoids are currently banned in flowering crops due to concerns about bee health

Bayer’s clothianidin does not have the same detrimental effect on bees as the other two neonicotinoid pesticides currently banned at EU level, new research has found.

Researchers behind the study said the findings showed a permanent ban on the chemical would be ’premature’.

But they said the findings showed the other two neonicotinoids currently banned across the EU, Bayer’s imidacloprid and Syngenta’s thiamethoxam, posed a ’threat’ to bee health at field level.

A senior figure at Syngenta has dismissed the findings, highlighting what he described as various ’inconsistencies’ in the research (see below).

Researchers from the University of Dundee and the University of St Andrews tested the impact of the chemicals on 75 bee colonies at five separate locations in Scotland.

They found clothianidin did not show the same detrimental effects on bee colonies as imidacloprid and thiamethoxam.

Dr Chris Connolly, from Dundee’s School of Medicine, who led the study, said:

“Our knowledge of the risk of neonicotinoids to bees is based on studies of imidacloprid and thiamethoxam and these findings have generally been extrapolated to clothianidin.

“However, in this study we have looked at the three neonicotinoids in parallel.

Further variation

"What we have found is that imidacloprid and thiamethoxam, but not clothiandin, exhibit toxicity to bumblebee colonies when exposed at field-relevant levels."

He said there was also further variation in the effects on bees between the three insecticides.

He added: "So we can clearly see that the banned neonicotinoids are not the same, so they should be considered independently when considering risk and legislation.

“From our findings, we consider that it is premature to place a permanent ban on the use of clothianidin. That said, a moratorium on its use should continue until the knowledge gaps are filled on its wider impact on other species.”

Dr Connolly said the study once again confirmed the threat to bumblebees from use of imidacloprid and thiamethoxam.

“We have seen further evidence to indicate the risk from these insecticides, including deficits in colony strength,” he said.

“Given these findings, small changes in the pesticide structure or its target site in insects are likely to be critical to risk assessment and each pesticide/insect combination needs to be considered independently - evidence should not be extrapolated to similar chemicals or insects.

"Real risk must be determined empirically.”

The results of the study are published in the journal Scientific Reports.

Reaction

Prof Lin Field, Head of Biological Chemistry and Crop Protection at Rothamsted Research ,said: “"It is especially interesting to see that at colony level one of the compounds, clothianidin, showed no detrimental effects.

"It is known that different neonicotinoids show different direct toxicity to bees, as do different members of other chemical classes (pyrethroids and organophosphates) so we should maybe not be surprised at these results.

“The authors are right to conclude that each pesticide/insect combination needs to be considered independently and we shouldn’t extrapolate across a chemical class or across species.

"The effect of a chemical on an insect will depend on many factors including differences in the chemical’s structure or the target site protein, in addition differential uptake and metabolism will affect toxicity.”

Dr Mike Garratt, an ecologist at the Centre for Agri-Environmental Research at the University of Reading, said: “This is an important and timely study.

"As the body of evidence for negative effects ofneonicotinoids on non-target species mounts, it is important to consider the differential effects of these chemicals and this new research clearly demonstrates not all are equally harmful.

“This study only considers impacts on one species of bumblebee. Similar variability in toxicity might be expected for other species of bee and non-target organism, and it is important to remember there are more than 200 distinct bee species in the UK alone.

“This work once more highlights the clear evidence gaps regarding the wider effect of this type of insecticide. Much more work needs to be done if these serious policy decisions, with wide-ranging impacts on our food supply and environment, are to be based on the best scientific evidence.”

“The paper attempts to link changes at the receptor level following exposure to threeneonicotinoid insecticides to short-term acute mortality and on through to the consequences on long-term colony health in bumble bees using continuous exposure to treated syrup.

There are a number of inconsistencies, over-interpretation of data, and the use of rather tenuous links (e.g. extrapolating effects of long-term nicotine effects in man to effects of neonicotinoid insecticides on bumble bees) to explain the results found.

"Inconsistencies include how thiamethoxam, but not clothiandin, has a negative effect at the colony level when clothiandin is a major metabolite of thiamethoxam formed in bumblebees, as shown in this study.

"The apparent colony effects reported in this study for thiamethoxam also contradict a previous study, which reported no adverse effects on bumble bee micro-colonies at similar levels of exposure over an extended period.

“It is important to note that the colony studies were conducted by directly feeding colonies with spiked sucrose, which is not representative of exposure of wild bumble bees under normal field conditions."

The colony level results reported from these studies are also inconsistent with other reported colony studies with bumble bees, probably due to the single post-exposure assessment point approach selected.

"The significant effect reported for thiamethoxam on ratio of males to females, nest size etc. could equally be attributed to the thiamethoxam colonies moving from colony growth mode to reproductive phase earlier than the other colonies."